Flow control valves used to hydraulically damp stochastic or periodic flow rate perturbations are used in such diverse devices as showerheads, nozzles and heating and cooling systems. In such devices it is desirable that the valves have a hydraulic loss coefficient proportional to a positive exponential power of the flow rate. Such valves are disclosed in U.S. Pat. Nos. 1,021,677; 1,211,583; 2,179,292; 2,555,803; 2,845,087; 3,659,433; 4,080,993; 4,082,225; and 4,244,526. In each of these valves the fundamental principle of operation is the control of flow rate by control of the flow area. In the valves disclosed in U.S. Pat. Nos. 2,179,292 and 4,082,225 a moveable object and an orifice or orifices are combined in the form of a spring loaded, slotted piston whose position relative to an enclosing stepped bore determines that position of the slots which is open for fluid flow. In the valves disclosed in the remaining cited patents, a moveable object is used with or without a tensioning spring to partially block a separate fixed oriface or orifaces. All of these valves have a common problem. Failure of the valve can result in a complete flow blockage by a broken component.
It has been observed that the hydraulic loss coefficient for flow of nonviscous fluid past two objects in a uniform channel having a Reynolds number greater than 1.times.10.sup.5 is an increasing function of the distance between the objects. See Handbook of Hydraulic Resistance: Coefficients of Local Resistance and of Friction, by I. E. Idel'chik. The hydraulic resistance of such an arrangement is directly proportional to the hydraulic loss coefficient. For example, for two identical cylindrical objects in a cylindrical channel as schematically illustrated in FIGS. 1(a) and 1(b), the hydraulic resistance R.sub.D is given by the following formula: ##EQU1## where C is the hydraulic loss coefficient, d is the diameter of the cylindrical objects and D is the diameter of the channel. Similarly, for two identical disc-shaped or spherically-shaped objects in a cylindrical channel as schematically illustrated in FIGS. 2(a) and 2(b), the hydraulic resistance R.sub.D is given by the following formula: ##EQU2##
As is shown in the graphs presented in FIGS. 1(c) and 2(c), which are based on experimental results published in Idel'chik, the hydraulic loss coefficient C for each of the two illustrative examples, as a function of ratios of the distance between the two objects to the diameter of the objects, is monotonicly increasing in the operating range indicated for a Reynolds number greater than 1.times.10.sup.5.
Two objects in a channel as illustrated may be used in a valve arrangement having a hydraulic loss coefficient which varies as a positive exponential power of the flow rate. Such a valve may be used to damp flow rate perturbations, including periodic variations. Since the diameter of the objects is characteristically less than that of the channel, there is no danger of a blockage to flow should one or both of the objects be damaged.